fix(mcp): accept JSON string for add_progress_event detail param

FastMCP validates dict | None strictly, rejecting a JSON string even if
parseable. Broaden to dict | str | None and coerce in the function body
so callers don't need to pre-parse the detail payload.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mcp_server/server.py

@@ -547,7 +547,7 @@ def add_progress_event(
     topic_id: str | None = None,
     workstream_id: str | None = None,
     task_id: str | None = None,
-    detail: dict | None = None,
+    detail: dict | str | None = None,
 ) -> str:
     """Append a progress event to the log.
 
@@ -557,8 +557,13 @@ def add_progress_event(
         topic_id: optional topic UUID
         workstream_id: optional workstream UUID
         task_id: optional task UUID
-        detail: optional structured data (JSONB)
+        detail: optional structured data (JSONB); accepts a dict or a JSON string
     """
+    if isinstance(detail, str):
+        try:
+            detail = json.loads(detail)
+        except (json.JSONDecodeError, ValueError):
+            detail = {"raw": detail}
     event = _post("/progress", {
         "topic_id": topic_id,
         "workstream_id": workstream_id,